Mario vs. Donkey Kong's pretty good for what it is: a level-based action/puzzle game.
If you've ever played Mario & Wario, chances are you'll like this game. Plus it's got the advantage of being an original, instead of a port/remake.
Of course, the other two games are awesome in their own right. Get one of them if you've never played its original, or if you have and just enjoy it too much.
Most people would favor SMB3, but I'm a bigger fan of Yoshi's Island, myself.
Go Moon!